Sustainable generation, transmission, distribution and utilization of energy have all become a priority for addressing global concerns in relation to both depletion and irresponsible use of fossil fuel reserves. Encouragements with intensives for wider exploitation of renewable resources can be considered as an integral part of this mission. As a result, over the past several years many large renewable energy plants have been built and incorporated into the main power network. This trend soon changed in favour of decentralized energy generation or sometimes referred to as distributed generation (DG). More recently, DG systems became Green Energy (GE) systems being solely based on renewable or Green energy sources through which more economic, environmental and sustainability benefits can be achieved. A GE system, which typically derives power from wind, solar or bio-gas, is operated at either medium or low power levels and allows the energy to be consumed or grid-connected at or near the point of generation. A medium power GE system is usually capable of supplying power for industry, large offices and community complexes, whilst a low power GE unit would be of a power level that is adequate to power either grid-connected or stand-alone houses, farms, lighthouses and telecommunications facilities.
Power generation through GE system is unpredictable in nature due mainly to the dependence of renewable energy sources on climate conditions. Some form of energy storage is therefore an essential and integral part of most, if not all, GE systems as it allows both storage and retrieval of energy when necessary. Electric Vehicles (EVs) have recently emerged as one way forward for clean or green transport, and also means for addressing energy fluctuations in the power network. The latter became popular as vehicle-to-grid (V2G) power. Although EVs are primarily considered as a method of clean transport, they can also be used in GE systems to supplement the energy storage, and such systems have been referred to as ‘Living & Mobility’. Irrespective of the application, an EV essentially requires some form of a power interface to the grid or power supply to charge its battery storage. In situations, where the battery storage of an EV is used for both V2G and G2V applications, or to supplement an existing battery storage as in the case of ‘Living & Mobility’, the power interface should necessarily be bi-directional to allow for both charging and discharging of the vehicle. A hard-wired power interface between the EV and the grid is simple and can be used to either charge or discharge batteries but such wired interfaces are now considered to be inconvenient and inflexible, and pose safety concerns. Wireless or contactless power interfaces have thus become an attractive alternative for charging and/or discharging EVs. Amongst the existing wireless power transfer technologies, Inductive power Transfer (IPT) is a key technology that has widely been accepted as suitable for charging/discharging EVs or V2G and G2V applications
IPT systems produce voltages and currents at a much higher frequency in contrast to low grid frequency. Therefore existing IPT systems essentially require an additional low-frequency DC-AC converter stage for grid integration with bi-directional power flow.
The additional converter stage with a DC link capacitor significantly increases the system cost and complexity, and reduces the efficiency and reliability.